[project @ 2003-07-21 15:14:18 by ross]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcMType.lhs

diff --git a/ghc/compiler/typecheck/TcMType.lhs b/ghc/compiler/typecheck/TcMType.lhs
index 3d9f210..207411c 100644 (file)
--- a/ghc/compiler/typecheck/TcMType.lhs
+++ b/ghc/compiler/typecheck/TcMType.lhs
@@ -11,7 +11,7 @@ module TcMType (
 
   --------------------------------
   -- Creating new mutable type variables
-  newTyVar, 
+  newTyVar, newSigTyVar,
   newTyVarTy,          -- Kind -> TcM TcType
   newTyVarTys,         -- Int -> Kind -> TcM [TcType]
   newKindVar, newKindVars, newOpenTypeKind,
@@ -112,6 +112,11 @@ newTyVar kind
   = newUnique  `thenM` \ uniq ->
     newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("t")) kind VanillaTv
 
+newSigTyVar :: Kind -> TcM TcTyVar
+newSigTyVar kind
+  = newUnique  `thenM` \ uniq ->
+    newMutTyVar (mkSystemTvNameEncoded uniq FSLIT("s")) kind SigTv
+
 newTyVarTy  :: Kind -> TcM TcType
 newTyVarTy kind
   = newTyVar kind      `thenM` \ tc_tyvar ->
@@ -744,13 +749,25 @@ kindErr kind       = ptext SLIT("Expecting an ordinary type, but found a type of
 %************************************************************************
 
 \begin{code}
+-- Enumerate the contexts in which a "source type", <S>, can occur
+--     Eq a 
+-- or  ?x::Int
+-- or  r <: {x::Int}
+-- or  (N a) where N is a newtype
+
 data SourceTyCtxt
   = ClassSCCtxt Name   -- Superclasses of clas
-  | SigmaCtxt          -- Context of a normal for-all type
-  | DataTyCtxt Name    -- Context of a data decl
+                       --      class <S> => C a where ...
+  | SigmaCtxt          -- Theta part of a normal for-all type
+                       --      f :: <S> => a -> a
+  | DataTyCtxt Name    -- Theta part of a data decl
+                       --      data <S> => T a = MkT a
   | TypeCtxt           -- Source type in an ordinary type
+                       --      f :: N a -> N a
   | InstThetaCtxt      -- Context of an instance decl
+                       --      instance <S> => C [a] where ...
   | InstHeadCtxt       -- Head of an instance decl
+                       --      instance ... => Eq a where ...
                
 pprSourceTyCtxt (ClassSCCtxt c) = ptext SLIT("the super-classes of class") <+> quotes (ppr c)
 pprSourceTyCtxt SigmaCtxt       = ptext SLIT("the context of a polymorphic type")